Why won't blender 2.8 bake more than 250 frames?
Blender has different simulation engines, and they have different cache length settings¹ (it's honestly true that these settings could be made more consistent...).

It appears that you have extended the cache length for the Rigid Body physics inside the Scene tab, but you actually wanted to extend the Cloth cache.

You find it here: under Physics > Cloth > Cache > End:



¹ fluid cache is bound to the Start/End of the animation; Rigid body cache is under the Scene settings; Soft body, Cloth and Smoke have their cache options in the relevant Physics tab for each object; particle cache lasts for the lifetime of the last emitted particle